Silane coupling agents having ambifunctionality are known in the art to provide a stable bond between two dissimilar substrates, usually organic to inorganic, such as organic polymers to inorganic substrates such as glass, mineral fillers, metals, and metallic oxides. The bond between the inorganic and the organic components generally result in greater strength and service life to the polymer.
Polymerizable silane coupling agents are commercially available from numerous sources. Despite their general availability, however, only nonfluorinated polymerizable silane coupling agents are known. The polymerizable group contains either (meth)acrylate, allyl, styryl, amino, or epoxy functionalities, while the silane group is usually an alkoxy silyl moiety (generally methoxy or ethoxy) which serves as a binding site to hydroxy-functional inorganic substrates via displacement of the alkoxy groups. Additional information concerning silane coupling agents may be found in the book by E. P. Pleuddeman ("Silane Coupling Agents", Plenum Press: New York, 1982, p 20).
Substitution of fluorine for hydrogen in polymers and coatings is often desirable to impart useful properties such as lower surface energy. Typically, incorporation of fluorine into polymers and coatings has been made by copolymerizing (meth)acrylate monomers derived from (meth)acrylic acid and highly fluorinated alcohols. However, (meth)acrylates often polymerize at slow rates and provide polymers which possess inadequate thermal and hydrolytic stabilities.
Fluorinated (meth)acrylamide monomers have been described in several patents. U.S. Pat. Nos. 2,743,297 and 3,997,604 disclose fluorinated (meth)acrylamide monomers prepared by the reaction of fluorinated secondary or primary amines and (meth)acryloyl chloride; a complication in the synthesis is the removal of by-product hydrogen chloride.
2-Alkenyl azlactones are known to react with certain nucleophiles such as primary amines and alcohols to afford (meth)acrylamide-functional products. It is disclosed in U.S. Pat. No. 4,931,582 that linear fluorinated-alcohols and -diols, when reacted with 2-alkenyl azlactones, yield desirable fluorinated, acrylamide-functional monomers.
Optical fibers and waveguides in their simplest construction consist of a so-called core material through which the majority of the optical information passes and, surrounding the core, a cladding material which transmits some of the light but whose principal function is to restrict the optical information to the core region of the construction.
Core materials have either been siliceous (glass) or organic polymer in nature. While certain advantages, such as outstanding flexural strength, ease of processing, and facile connectorization attend organic polymer cores, glass cores are virtually unchallenged in their ability to transmit optical information with a low degree of attenuation or loss. Therefore, considerable effort has been made in the art to utilize glass cores despite obvious drawbacks such as brittleness, moisture sensitivity, and extreme processing conditions.
Effective cladding materials exhibit low refractive indices and low moisture vapor transmission rates. Fluorinated polymer claddings have been described to meet these criteria on both organic polymer cores (for example, in U.S. Pat. Nos. 4,505,543; 4,544,235; 4,557,562; 4,660,923; 4,687,295; 4,720,428; and 4,836,642) and glass cores (for example, in Eur. Patent Appl. 128,516; Eur. Patent Appl. 239,935; U.S. Pat. No. 4,804,246). A problem with these fluorinated polymer systems, however, is that they are applied to the core material either from solution which can be polluting to the environment and require complete outgassing of even the last traces of solvent for optimum performance or are melt extruded onto the core which can be very physically damaging to the surface of the core.
An innovation in the fiber optics industry was put forth in U.S. Pat. No. 4,511,209 describing so-called "hard clad silica" (HCS) fibers that were cured by ultraviolet light. Earlier approaches to UV curable cladding/buffer materials had stressed that the cladding or primary coating should be very elastomeric and possess a low modulus, while the buffer or secondary protective coating should be a tough, high modulus material. These precepts for so-called "plastic clad silica (PCS) fibers usually involved very low modulus silicone cladding materials and are described, for example, by L. L. Blyer, Jr., et. al., " Polymers for High Technology", ACS Symp. Ser. 346, edited by M. J. Bowden and S. R. Turner, published by the American Chemical Society: Washington, D.C., Chapter 34, pp 410-416, 1987. In contrast, HCS fibers (further described by W. B. Beck and M. H. Hodge, "Laser Focus/Electrooptics", pp 90-96 (1984) and by B. J. Skutnik, et. al., Mat. Res. Symp. Proc., 1987, 88, 27) feature a hard polymer cladding that is chemically bonded to a glass core.
Earlier, we disclosed in U.S. Pat. No. 4,968,116 a fluorinated cladding system that comprised 40 to 95% by weight of a fluorinated acrylate, from 2 to 35% by weight of a polyfunctional crosslinking acrylate being difunctional or higher, and a photoinitiator. We further disclosed that the addition of a vinyl functionalized component such as (meth)acrylic silanes and (meth)acrylic acid enhances the adhesion to the core material. Krohn et. al., ISA Proceedings, 1990, 1633; describes that the above clad fiber provides: chemical resistance to most polar (water, acids) and non-polar (acetone, oils) solvents; increased stress corrosion resistance of the fiber, providing longer service life; and superior low temperature performance. In U.S. Pat. No. 4,971,424, we also disclose compositions which are viscous liquids at ambient temperatures of 20.degree.-30.degree. C. and are useful as cladding materials for optical fibers and waveguides.
The above-mentioned cladding compositions provide optical fibers which are useful for transmitting optical information and have numerical apertures (NA) generally in the range of 0.35-0.39.
Skutnik, B. J. et al., in "Dual Clad (Coat) Pure Silica Optical Fibers for Biosensors/Endoscopes" SPIE Vol. 1067 Optical Fibers in Medicine IV (1989) p 22 describes high NA optical fibers.
Materials have been utilized to achieve a high NA optical fiber. Aleksandrov et al. (Soviet J. Ouantum Electronics, 1980, 10, 105) have suggested the use of organic silicone compounds to yield high NA optical fibers. Organopolysiloxane claddings have been described to meet these criteria (for example, in Eur. Patent Appl. 208,239 and U.S. Pat. No. 4,317,616). A problem with these organopolysiloxane systems, however, is that they are applied to the core material from solution (vide supra). Low refractive index inorganic materials such as boron, fluorine, etc. have been used as claddings to obtain high NA optical fibers utilizing the so-called chemical vapor deposition (CVD) techniques. For example, in U.S. Pat. No. 4,277,270 use of barium, sodium, boron, and arsenic was disclosed to form a multicomponent glass core with a NA value of 0.49. Problems encountered with these glass-glass systems include very expensive and elaborate CVD equipment which is needed to dope the glass core with the inorganic substance.
Plastic optical fibers such as polymethyl methacrylate have high NA values. However, these fibers are limited in use since high temperature applications cannot be achieved and optical loss values are extremely high when utilizing long lengths for data transmission.